As shown in FIG. 1, the main control part of existing electronic switch applied to a lithium battery powered tool consists mainly of a combination of a Micro Controller Unit (MCU/singlechip), a DC voltage-stabilized power supply (LDO) and a Pulse Width Modulation (PWM) driving circuit.
The micro controller unit, the voltage-stabilized power supply and the PWM driving circuit in the main controller part of the electronic switch are separated from each other and work based on the following principle: the DC voltage-stabilized power supply (LDO) provides a stable working power supply to the singlechip so that the singlechip can run smoothly to collect the voltage signal and the temperature signal of the lithium battery, a speed-governing potentiometer signal and the current signal of a load, process the signals collected and output a PWM signal for controlling the rotation speed of a motor using a motor/load PWM driving module and, if needed, the working state of a working lamp through an I/O port at the same time.
With a plurality of electronic parts and components, the electronic switch is complicated in circuit design, large in Printed Circuit Board Assembly (PCBA) size and high in production cost.
FIG. 2 is a schematic diagram illustrating existing PWM signal. As shown in FIG. 2, the PWM signal of existing electronic switch is the single segment from (x1, y1) to (x2, y2) displayed in the single-segment linear control chart.
In FIG. 2, taking the travel of a switch as an x axis and a PWM duty cycle (PWM duty) output as a y axis, it can be obtained according to FIG. 2 that in the PWM output control curve of existing switch, y and x meet the following relationship:Y=0% when x<x1;Y=k1*x+b1 when x1≦x<x2, in which k1=(y2−y1)/(x2−x1);b1=(y1−k1*x1);y=100% when x≧x2.
As such a PWM output control curve is a single-segment linear control, that is, the segment from (x1, y1) to (x2, y2) shown in FIG. 2 is a straight line segment, it can be known that the PWM duty output is already great when the travel of a speed-governing potentiometer is short, resulting in that a motor rotates at a relatively high rotation and vibrates, thus, the user cannot position the target working point correctly with an electric tool (e.g. an electric drill or electric hammer), causing inconvenience in the use of the electric tool.
Further, the power of a battery cannot be obtained with existing electronic switch, additionally, more expense is cost to exchange interfaces or increase connector devices when a device interface for collecting parameters of a battery or load is not matched with the input interface of existing electronic switch as existing electronic switch is poor in connection matching with other devices and is time-costing and effort-costing when being connected with other devices.
It can be known from above that existing electronic switch, which is provided with a great many of electronic components and the control curve of which is a single-segment linear control, is complicated in design, difficult in PCB wiring and short in low-speed travel and is consequentially bulky and incapable of controlling the working of an electric device at an accurate working point.
No effective solution has been proposed to address the problem that existing electronic switch, which is provided with a great many of electronic components and the control curve of which is a single-segment linear control, is complicated in design, difficult in PCB wiring and short in low-speed travel and is consequentially bulky and incapable of controlling the working of an electric device at an accurate working point.